The invention relates to a pump with a housing, having an inlet and an outlet, a fixed cylinder central to a mid-axis of the pump, a displacer, planetating eccentrically within the cylinder, a crank drive for the displacer, a circumferential sickle-shaped pumping chamber between the cylinder and displacer and a helical sealing element in the pumping chamber. Moreover, the present invention relates to a method for operating such a pump.
A pump having the characteristics mentioned is known from U.S. Pat. No. 5,174,737. It has the function of a compressor and is preferably intended for compressing the gas of a refrigerant circuit.
It is the task of the present invention to design a pump of the aforementioned kind such that it may be employed as a dry running vacuum pump.
Over the past years, the customers have required from the manufacturers of vacuum pumps, dry running vacuum pumps at an increasing rate. These are to be understood as pumps, the pumping chambers of which are free of lubricant. In the instance of pumps of this kind there no longer exists the risk of hydrocarbons diffusing into the chambers to be evacuated by the pumps and thereby impairing the processes (semiconductor production, evaporation processes, chemical processes etc.) being performed within the chambers.
Dry running rotary vane pumps are known. The parts (vanes, inside wall of the pumping chamber) which slide under friction exhibit a comparatively high relative velocity. For this reason, the service life of the vanes and thus the pumps themselves is limited. Scroll vacuum pumps are better suited for dry operation. These comprise a fixed and a revolving component which support helical pumping elements engaging into each other. Their manufacturing costs are high. Moreover, they need to be subjected to maintenance frequently so as to ensure reliable continuous operation. Also dry piston vacuum pumps are offered on the market. Their manufacturing costs are also high, their construction volume is large. Other disadvantages are noise production and the unavoidable vibrations. Finally, dry two-shaft vacuum pumps (screw, Roots, claws vacuum pumps) are known. These offer pumping capacities commencing at approximately 20 m3/h. Manufacture and deployment of vacuum pumps of this kind is usually, however, no longer economical at pumping capacities below 50 m3/h.